Methods and equipment for forming tubes of fibrous material

ABSTRACT

Equipment for forming a tubular rod of fibrous material comprises: a gathering station constructed to receive a continuous supply of fibres and to gather the fibres into a bundle as the fibres advance through the equipment; a divider arranged in the path of the fibres through the equipment and constructed to from a cleft along the length of the bundle as it advances through the equipment; a mandrel positioned in the path of the bundle of fibres in alignment with the divider and constructed to form the cleft into a passage through the bundle of fibres as the bundle of fibres advances over the mandrel; and a die constructed and arranged to cooperate with the mandrel to form the fibres in a tubular configuration around the mandrel.

FIELD OF THE INVENTION

This patent specification relates to methods and equipment for formingtubes of fibrous material, in particular tubular filter rods for use incigarettes

BACKGROUND

Tubular rods of fibrous material can be formed by gathering fibres intoan elongated bundle, forming the fibres of the bundle around a mandrelin a tubular configuration, and separating the resulting fibres from themandrel as a tubular rod with a central axial passage. However, wherethe bundle of fibres is formed around the mandrel in a continuousprocess, the bundle may from time to time become misaligned with themandrel due to variations in the density fibres within the bundle, withthe result that the axis of the central passage becomes misaligned withthe central axis of the tube, so that the wall thickness of the tube isnot uniform, or the tubular configuration collapses completely. Theprocess and equipment must then be halted and restarted, causing delaysand additional costs in production. This happens particularly if thebundle of fibres is gathered from a feed stock of fibres of low density,or if the tubes are formed at higher speeds.

SUMMARY

In one embodiment, a method of forming a tubular rod of fibrous materialcomprises gathering fibres into an elongated bundle, parting the fibresto form a cleft along the length of the bundle, introducing a mandrelinto the cleft, closing the fibres of the bundle around the mandrel in atubular configuration, and separating the fibres from the mandrel as atubular rod.

In another embodiment, a continuous manufacturing process for producinga tubular rod of fibrous material comprises gathering the fibres into abundle, parting the fibres along the length of the bundle advances toform a radial cleft, advancing the bundle over a mandrel positioned inthe recess, closing the fibres of the bundle around the mandrel,treating the bundle to form a stable tubular configuration, and removingthe bundle from the mandrel.

Treatment of the bundle of fibres may for example comprise advancing thebundle through a constriction that defines a desired circumferentialprofile for the bundle of fibres, and introducing a treatment fluid forcuring the fibres introduced into the bundle as the fibres enter theconstriction.

In another embodiment, equipment for forming a tubular rod of fibrousmaterial comprises gathering equipment constructed to receive acontinuous supply of fibres and to gather the fibres into a bundle asthe fibres advance through the equipment; a divider arranged in the pathof the fibres through the equipment and constructed to from a cleftalong the length of the bundle as it advances through the equipment; amandrel positioned in the path of the bundle of fibres in alignment withthe divider and constructed to form the cleft into a passage through thebundle of fibres as the bundle of fibres advances over the mandrel; anda die constructed and arranged to cooperate with the mandrel to form thefibres in a tubular configuration around the mandrel.

In one embodiment, the die has a central passage there through, and themandrel comprises a rod mounted within the central passage to define anannular space between the die and the mandrel.

The equipment may further comprise treatment equipment constructed andarranged to cure or fix the fibres in the tubular configuration. Theconstruction of the treatment equipment will vary according to thenature of the fibrous material and the technique used to fix the finalform of the bundle of fibres. For example, the fibres may be formed froma thermoplastics material that can be softened by the application ofheat, causing the fibres to fuse together at their points of contact.With such fibres, the treatment station is constructed to apply heat tothe fibres whilst supported on the mandrel. For this purpose, thetreatment station may comprise a steam chamber constructed toaccommodate the passage of the fibres therethrough.

In one embodiment, the treatment station comprises a housing defining achamber into which a treatment fluid may be introduced, and the die ispositioned within the housing and is provided with one or more conduitsfor delivering the treatment fluid from the chamber to the fibres.

The formation of a cleft in the fibrous bundle prior to introduction ofthe mandrel facilitates the formation of a tube, and reduces the risk offailure as a result of misalignment of the mandrel with the bundle offibres.

The cleft may divide the bundle into separate parts, e.g. two distinctbundles, or, alternatively the cleft may be in the form of a recessextending partially through the bundle, e.g. radially from the peripherytowards the centre of the bundle, for example 20%, 30%, 40%, 50% 60%,70% or 80% through the thickness of the bundle.

The method and equipment disclosed herein may be used to process fibresfrom a feedstock of fibrous material, e.g. a bale of fibre tow, or fromfibres supplied directly from a continuous manufacturing process orequipment, e.g. by melt-blowing, melt-spinning, electro-spinningprocesses and equipment, or by other processes or equipment forproducing fibres know to those skilled in the art. A web of entangledfibres produced in any of these ways, or by another process, may then begathered into an elongated bundle using the method or equipmentdisclosed herein.

Fibre tow is formed from crimped fibres, for example of celluloseacetate. The crimping of the fibres increases the elasticity of thefibrous bundle therefrom (i.e. the extent to which the fibres can bestretched without breaking). This in turn affects the resilience of thetubes or rods formed therefrom. In a bale of tow, the fibres are highlycrimpled. Before use, the tow is usually “bloomed”, or treated to reducethe crimping, and to release the fibres from each other. The crimp isnot entirely eliminated from the fibres. A degree of crimping of thefibres provides elasticity to the tow material, which facilitates theformation of the fibre bundle into the desired shape, such as a rod or atube.

The method and equipment disclosed herein are exemplified by theproduction of fibres by melt-blowing. In a typical melt blowing process,fibre-forming polymer is extruded from one or more orifices intoconvergent streams of hot gas (for example air or possibly an inertgas). The gas streams blow the polymer emerging from the orifices intothin streams of molten polymer, which then solidify to form smalldiameter fibres of filaments. The fibres are entrained in the stream ofgas and may be collected, for example by directing the stream of gas andfibres on to a collection surface. In contrast to tow fibres, meltblownfibres are essentially linear, and uncrimped. A bundle of meltblownfibres therefore has relatively low elasticity and the individual fibresare more prone to breaking. Elasticity in a bundle of meltblown fibresarises primarily from the tangled web structure of the bundle that iscreated by the accumulation of the fibres into a web, mat or bundle.

Application of heat to the web, for example by heated treatment fluidsuch as steam or water vapour in air or an inert gas, lubricates thefibres and facilitates disentanglement and formation of a more orderedweb of the fibres for formation into a desired linear structure such asa rod or tube.

When the bundle fibres is passed through a die, the application of heatcauses the fibre bundle to stretch. The longer the fibres remain in theforming section of the die, the more the fibre bundle stretches. Theextent to which the fibre bundle is stretched in the die affects thefinal density, shape, size and structure of the finished product.

A plasticiser may be used to facilitate the curing of the fibre bundleinto a formed shape by bonding together at their points of contact. Theplasticiser may be applied to the fibre bundle, for example by spraying.This technique is commonly used on crimped fibre tow. For meltblownfibres, the plasticiser is commonly incorporated in the polymer materialfrom which the fibres are formed and is released therefrom on theapplication of heat to the fibres sufficient to cause the polymer tosoften or to melt.

In one embodiment, the gathering station or equipment may be of aconstruction typically used in equipment in this field and known as aforming cone. The forming cone may for example comprise a structure thatdefines a longitudinally extending passage of tapering configurationbetween an inlet for receiving the fibres and an outlet from which theweb of fibres may be withdrawn as a bundle.

The divider may comprise a wall, pin, blade, plough or other formationmounted in the path of the fibres through the equipment, upstream of themandrel. The divider may be shaped at its upstream end to facilitate theformation of a cleft in the bundle fibres. For example, the divider maypresent a curved or v-shaped face or edge to the bundle of fibres. Inone embodiment the divider is positioned in the forming cone. Forexample, in one embodiment the divider comprises a wall in the passageof the forming cone extending between the inlet and the outlet.

In one embodiment, equipment for forming a web of fibres comprises aforming cone having an inlet for receiving a web of fibres, an outletfrom which the web of fibres may be withdrawn as a bundle and defining alongitudinally extending passage of tapering configuration between theinlet and the outlet, the forming cone having a divider positionedwithin the passage and projecting across the outlet to form alongitudinally extending cleft in the bundle of fibres.

The equipment may comprise a mandrel positioned in alignment with theoutlet of the forming cone to receive the bundle of fibres from theoutlet of the forming cone and around which a central passage may beformed in the bundle of fibres.

In one embodiment of the equipment, the mandrel is mounted in a tubularcasing mounted around the path of the bundle of fibres through themachine. The mandrel may for example comprise a rod that is elongated inthe direction of movement of the bundle of fibres and mounted in thetube along an axis coincidental or parallel to the axis of the tubularcasing. In an embodiment with such a construction, the divider maycomprise a support connecting the mandrel to the tubular casing.

In one embodiment, the mandrel may be configured to deliver treatmentfluid, such as steam or hot water vapour, to the fibres as a bundle ofthe fibres passes over the mandrel. For example, the mandrel may beprovided with a passage having an inlet for the introduction of thetreatment fluid and an outlet communicating with surface of the mandrel.

This specification also discloses a method of forming a tubular rod offibrous material comprising gathering fibres into an elongated bundle,closing the fibres of the bundle around the mandrel in a tubularconfiguration, and separating the fibres from the mandrel as a tubularrod, wherein a treatment fluid is introduced into the bundle through themandrel.

This specification further discloses equipment for forming a tubular rodof fibrous material comprising a mandrel constructed to form a passagethrough the bundle of fibres as the bundle of fibres advances over themandrel, wherein the mandrel is provided with a passage having an inletfor the introduction of the treatment fluid and an outlet communicatingwith surface of the mandrel.

The formation of the fibres into a rod or tube around the mandrel may orbe facilitated if the treatment fluid is introduced in a direction thatis not opposed to the direction of movement of the bundle over themandrel. For example, the passage in the mandrel may be arranged todischarge fluid in a direction generally radially, or generally at rightangles to the direction of movement of the fibres, at an acute anglethereto, for example at an angle not significantly greater than 90° tothe direction of movement of the bundle of fibres, possibly 10, 20, 30,40, 50, 60, 70, or 80 degrees to the direction of movement. In theseconfigurations, the fluid is directed in to the fibre bundle generallyin the downstream direction. Even if directed at angles marginallygreater than 90° (e.g. up to 95° to the direction of movement), thefluid flow may not significantly oppose the movement of the bundle offibres over the mandrel, and the kinetic energy of the stream of fluidmay still assist the compression and shaping of the bundle of fibresaround and over the mandrel. At directions significantly greater than90°, e.g. from 100 to 180°, component of the force exerted on the fibresby the fluid will become significantly contrary to the movement of thefibre bundle over the mandrel and will oppose compression and shaping ofthe fibre bundle.

Embodiments of the equipment and methods will now be described, by wayof example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side elevation, partly in vertical cross section,and cut to reduce the width, of an embodiment of equipment for forming atubular rod of fibrous material;

FIG. 2 is a schematic plan of the equipment of FIG. 1;

FIG. 3 is an exploded view of an embodiment of a forming cone that maybe used in the equipment of FIGS. 1 and 2;

FIG. 3A is a perspective view, on an enlarged scale, of one component ofthe forming cone of FIG. 3;

FIG. 4A is an elevation of the upper part of the forming cone of FIG. 3from one end;

FIG. 4B is a plan from below of the part shown in FIG. 4A;

FIG. 4C is an elevation of the part shown in FIG. 4A from the oppositeend;

FIG. 5A is a perspective view from above and one end, on an enlargedscale, of embodiments of a mandrel assembly and a treatment assemblythat may be used in the equipment of FIGS. 1 and 2;

FIG. 5B is a longitudinal vertical cross-section of the assemblies ofFIG. 5A;

FIG. 5C is a side elevation of the equipment shown in FIGS. 5A and 5B,with the assemblies separated from each other;

FIG. 5D is a longitudinal cross-section similar to that of FIG. 5B ofthe equipment of FIG. 1 carrying an alternative embodiment of a mandrelassembly;

FIG. 5E is an end elevation of the mandrel assembly of FIG. 5D installedon the equipment, viewed from upstream;

FIG. 6A is an exploded perspective view from above and one end of thetreatment assembly of FIG. 5A, separated from the mandrel assembly;

FIG. 6B is a vertical cross section through the assembly of FIG. 6A inthe direction of arrows 6B-6B;

FIGS. 7A to 7G illustrate, in cross section, and perspective, theenvelope of a bundle of fibrous material as successive stages to as itadvances through the equipment of FIGS. 1 to 6B, taken along lines 7A,7B, 7C, 7D, 7E, 7F and 7G of FIG. 1, in the upstream and downstreamdirections as indicated by the arrows, FIGS. 7A and 7B FIGS. 7C to 7Gshowing the bundle approximately to the same scale as each other, butreduced with respect to FIGS. 7A and 7B.

Referring to FIGS. 1 and 2, the equipment illustrated is of modularconstruction and comprises a continuously operable fibre supply module1, a fibre gathering module 2, in which the fibres are gathered into abundle in the form of a continuous web, and a forming module 3 in whichthe bundle of fibres is formed continuously into a rod in the form of ahollow tube 5. In in this example the fibrous tube produced is suitablefor use in the manufacture of filters for cigarettes.

Fibre Supply Module

The fibre supply module 1 comprises a melt-blowing head 10, theconstruction and operation of which will be familiar to persons skilledin the art, and is not illustrated in detail. In other embodiments, thefibre supply module may for example comprise a melt-spinning or anelectro-spinning unit, or a feed system for the supply of an expandedweb of fibres from a bale of filter tow material.

In the melt-blowing equipment illustrated, molten polymer material isfed into the melt-blowing head 10 through a polymer inlet manifold 12and emerges from the head at an array of jets 13. Hot pressurised gas,normally air, may be introduced into the melt blowing head 10 throughair inlet manifolds 14, 14 on either side of the polymer inlet manifold12 and emerges from the array of jets in two convergent high velocitygas streams. The streams of hot gas blow the polymer emerging from thearray of jets 13 into thin streams of molten polymer, which solidifywithin a few centimetres of the jets to form a multiplicity ofcontinuous small diameter fibres 15. A complex pattern of entangledfibres entrained within a fast-flowing stream of gas is thereby formed.

The gathering module 2 is arranged vertically beneath the melt blowinghead 10 to receive the fibres 15 entrained in the air stream from thehead. The vertical distance between the melt blowing head and the fibregathering module is exaggerated in FIG. 1 for clarity.

Fibre Gathering Module

The fibre gathering module 2 comprises a rigid frame 20 supporting ahollow casing 22 formed from metal plates welded or bolted together andsecured to the supporting frame 22. The casing 22 is generallyrectangular in plan with its major axis extending horizontally in alongitudinal direction from an upstream end, at the right-hand side ofFIG. 1, to a downstream end, to the left in FIG. 1.

A conveyor 24 mounted on the casing 22 provides a transport system formoving fibres 15 from the melt blowing head 10 part of the way along apathway 25 (the envelope of which is indicated by broken lines in FIG. 1and partially in FIG. 2) through the fibre gathering module 2 to the rodforming module 3. The conveyor 24 comprises a tensioning roller 26 ofrelatively large diameter mounted in bearings fixed to the upstream endof the casing 22 for rotation about a horizontal axis that extendstransversely of the casing. At the downstream end of the casing 22, anidler roller 27 and a drive roller 28, each of smaller diameter than thetensioning roller, are mounted in bearings fixed to the casing 22 forrotation about horizontal axes parallel to that of the tensioning roller26, the idler roller 27 being mounted above and upstream of the driveroller 28. An electrical drive motor (not shown) is mounted in thedownstream end of the casing 22 to rotate the drive roller 28 about itsaxis in an anticlockwise direction as seen in FIG. 1.

The three rollers 26, 27, 28 support a conveyor belt 29 of endlessconstruction having an upper run that extends in the longitudinaldirection of the casing 24 from the tensioning roller 26 along the uppersurface of the casing 22 to the idler roller 27, downwardly and aroundthe drive roller 28, and then back to the tensioning roller 26 in alower run parallel to the upper run. The idler roller and the tensioningroller may be adjusted in their bearings to align the upper runaccurately with the upper surface of the casing 22 and to providesufficient tension in the conveyor belt.

The conveyor belt 29 is constructed to allow the passage of gas throughthe belt whilst fibrous material entrained with the gas is deposited andretained on its surface as a web of entangled fibres. For example, theconveyor belt 29, or at least part thereof, particularly the centralregion extending the length of the belt, may be provided withperforations, slots or apertures, or is otherwise made porous, to allowthe passage of gas therethrough whilst supporting fibres 15 on itssurface. For this purpose, the conveyor belt may for example be a fabricmaterial woven to a density sufficient to permit a desired flow of gastherethrough under pressure.

The upper surface of the casing 22 is provided with apertures or slotsthat lie beneath the upper run of the conveyor belt 29, allowing gas topass through the conveyor belt into the interior of the casing 22, fromwhich air may be evacuated by a vacuum pump (not shown) and dischargedaway from the equipment. The portions of the upper surface of the casingimmediately surrounding the apertures or slots provide support for theupper run of the conveyor belt 29.

Fibre Forming Module

The forming module 3 comprises a rigid frame 40 supporting a number ofcomponents of rod-forming equipment, for transforming the bundle offibres 15 into the hollow tube 5, and a control panel 42 therefor. Therod forming equipment comprises a forming cone 50, a mandrel assembly 60and a treatment assembly 80. The forming cone 50 is fixed to the frame40 in alignment with the conveyor 24 of the gathering module 2. Themandrel assembly 60 and the treatment assembly 80 are adjustably mountedon a rail 43 in the form of an upwardly-open channel, which is securedto the frame 40 in alignment with the linear path of the fibres throughthe fibre gathering module 2. The longitudinal positions of the mandreland treatment assemblies 60, 80 along the rail may be adjusted relativeto each other and the forming cone as required to match the prevailingoperating conditions of the equipment.

Forming Cone

Referring to FIGS. 3, 3A, 4A, 4B and 4C, the forming cone 50 comprisesupper and lower half shells 51, 52 each being generally triangular inplan, and having a flat outer surface and a recessed inner surface. Thehalf shells are secured together by bolts 53. The inner surfaces of thehalf shells together define a smoothly tapering central passage 55extending from a generally rectangular upstream inlet 56 to a downstreamoutlet 57, which is in the form of a cylindrical tube of circularcross-section. A tubular outlet extension piece 58 (FIGS. 3 and 3A) isbolted to the half shells 51,52 in axial alignment with the outlet 57.

The inlet 56 is arranged to receive the gathered fibres 15 in the formof a flattened mat or web directly from the conveyor 24 of the fibregathering module. The tapered central passage is shaped and arranged tocompress the fibres and shape the web into a cylindrical shape as thefibres advance through the forming cone towards the outlet 57.

The interior surface of the upper half shell 51 is provided with adivider in the form of a rib 59 that projects radially inwardly towardsthe axis of the central passage 55 into the path of the fibres throughthe forming cone, and extends longitudinally from the inlet 56 andthrough the cylindrical tube of the outlet 57. The dividing rib 59 isnarrow compared with the diameter of the outlet of the forming cone sothat, as the bundle of fibres passes through the forming cone, thedivider forms a gap or cleft along the length of the bundle. In order tofacilitate the flow of the fibre bundle over the divider, the upstreamend 59 a of the rib is curved so that the extent to which the rib 59projects radially towards the axis of the passage increases smoothly andprogressively along the rib to a point A positioned inwardly of theinlet 56 at a distance of about 10 to 20% of the overall length of thedivider. From this point A and downstream thereof, the rib extendsmarginally beyond the centre of the passage through the forming cone.The rib may for example have a radial projection marginally greater than50% of the diameter of the outlet, for example up to 55%, 60% or 65% ofthe diameter of the outlet, depending upon the desired internal diameterof the finished tube formed from the fibres.

The outlet extension piece 58 is also formed with an axial internal rib59 a that has the same radial length and lies in the same plane as therib 59 within the upper half shell, thereby forming a continuation ofthe divider in the upper half shell 51.

Mandrel Assembly

Referring to FIGS. 5A and 5B, the mandrel assembly 60 comprises acarriage 61 that is mounted for sliding movement along the upstream partof the rail 43 and supported by parallel guides 48, 48 attached to eachside of the rail 43. The carriage includes a rack 62, which is receivedwithin the channel formed by the rail 43 and engages with a pinion wheel63 mounted on the rail 43 for rotation about a transverse axis by ahand-wheel 64, enabling the mandrel assembly to be moved longitudinallyback and forth along the rail 43 into a desired position in relation tothe treatment assembly 80 and the forming cone 50.

The carriage 61 also includes a horizontal guide 65 for a first slideblock 65 a that is mounted in the guide for transverse movement relativeto the carriage 61. The transverse position of the first slide blockwithin the horizontal guide may be adjusted and fixed by means of alocking bolt 66. The first slide block 65 a supports a vertical guide 67for a second slide block 67 a that is mounted therein for verticalmovement relative to the carriage 61. The vertical position of thesecond slide block 67 a within the vertical guide 67 may be adjusted andfixed by means of a locking bolt 68. The second slide block 67 a carriesa bracket 69 which in turn supports an axially-oriented tubular casing71 which is open at each end. The casing houses a mandrel, indicatedgenerally at 73, in the form of an elongated rod extending along thecentral axis of the casing 71. The longitudinal, vertical and horizontalposition of the mandrel may therefore be set precisely relative to theforming cone and the treatment assembly 80 by movement of the carriagelongitudinally along the track, and by adjustment of the first andsecond slide blocks 65 a and 65 b.

The tubular casing 71 for the mandrel 73 is generally square in externalcross-section, with bevelled edges along its length, and generallycylindrical in internal cross-section, with a counterbore 75 in theupstream end of larger internal diameter than the downstream end of thecasing. The casing 71 is secured to the bracket 69 by two bolts, and isaligned in the longitudinal direction, i.e. with its central axisarranged in the direction of travel of the bundle of fibres through theequipment.

A tubular mandrel support 72 is mounted within the counterbore 75 of thecasing 71. The mandrel support has an external diameter conforming tothe internal diameter of the counterbore 75 and is provided internallywith a bracket or carrier for the mandrel 73. In this embodiment, thebracket is in the form of a divider plate 78 that projects radiallyinwardly from the internal surface of the mandrel support 72 and extendsaxially within the support from the upstream end thereof. The rotationalposition of the mandrel support 72 within the casing 71 is adjusted suchthat the plate 78 lies in a desired radial orientation, in this casevertical. The radial extremity of the divider plate 78 is connected tothe mandrel 73 and may for example be formed integrally therewith as amoulding.

The mandrel 73 comprises an elongated cylindrical rod which, for ease ofassembly is made in two parts arranged coaxially, an upper mandrel rod73 a and a lower mandrel rod 73 b. The upper rod 73 a is of uniformradial cross section with a diameter greater than the thickness of thedivider plate to which it is connected, and is positioned by the platealong the central axis of the mandrel support 72 to project downstreaminto the support 72. The upstream end of the upper mandrel rodterminates in a domed portion or boss 76 that projects upstream, beyondthe mandrel support into the path of travel of the bundle of fibres. Thedownstream end of the upper mandrel rod 73 a is provided with aninternally-threaded aperture, which extends parallel to the central axisof the rod.

The lower mandrel rod 72 b has a cylindrical segment at its upstream endthat corresponds in diameter to the upper mandrel rod 73 a and, at itsdownstream end, a cylindrical segment 73 c of reduced diameter, whichcorresponds to the desired internal diameter of the finished tubularfilter rod 5. The two cylindrical segments of the lower mandrel rod areconnected smoothly to each other by a tapered intermediate segment, asillustrated. The upstream end of the lower mandrel rod 73 b carries athreaded axial bolt, which is received in the threaded aperture in thedownstream end of the upper mandrel rod 73 a, thereby fixing the twoparts of the mandrel in coaxial alignment within the mandrel support 72and the casing 71. The lower mandrel rod 73 b may be removed andreplaced by a similar component having a downstream end of a differentdiameter, according to the desired dimensions of the finished tubularrod 5.

The mandrel assembly 60 is configured to receive the bundle of fibresemerging from the outlet of the forming cone 50. The divider plate 78 ofthe mandrel support 72 is aligned radially with the divider ribs 59, 59a in the forming cone 50 and outlet extension piece 58 so that, as thebundle of fibres passes through the casing, the divider plate 78maintains the formation of the cleft along the length of the bundle, asthe domed portion 76 on the upstream extremity of the mandrel 73 plateis inserted into the cleft at the centre of the bundle of fibres. Thedivider plate 78 therefore serves the dual function of a bracket thatcarries the mandrel, and a divider for keeping open the cleft in thefibres formed upstream thereof.

Alternative Mandrel Assembly

An alternative mandrel assembly 60 for use in the equipment is describedbelow, with reference to FIGS. 5D and 5E. The mandrel assembly 60 is ofsimilar construction to that described with reference to FIGS. 5A, 5Band 5C, and in the drawings like parts are indicated by the samereference numerals.

In the mandrel assembly 60 of FIGS. 5D and 5E, the mandrel 73 ismodified to enable a gaseous or liquid treatment fluid, e.g. steam orwater vapour, to be delivered to the fibre bundle as the bundle passedover the mandrel. To this end, the upstream end of the casing 71 isprovided on its upper surface with an inlet for a steam line (notshown). The inlet comprises a gas-tight connection 90 having a centralpassage that communicates with a radial bore 92 in the divider plate 78.The bore 92 extends radially downwardly to the centre line of themandrel, where the bore communicates with a central axial passage 94 inthe upper mandrel rod 73 a. The axial passage 94 extends to the threadedaperture in the downstream end of the upper mandrel rod. The lowermandrel rod 73 b is likewise provided with a central axial passage 95,which is aligned with the passage 94 in the upper mandrel rod 73 a. Theaxial passage 95 extends through the threaded bolt 77 on the upstreamend of the lower mandrel rod and terminates at the centre of the taperedintermediate segment 74 of the mandrel. The intermediate segment 74 isprovided with four outlet vents 79 that connect the axial 95 to theexternal surface of the lower mandrel rod in order to discharge thetreatment fluid into the fibre supported on the mandrel 73. The ventsare disposed at equiangular intervals (90°) around the axis of themandrel and are inclined in the downstream direction at an angle of20-70° to the central axis of the mandrel in the direction of movementof the fibre bundle over the mandrel.

In this embodiment, steam or other treatment fluid may be fed into themandrel 73 through the connector 90. The steam may then pass to thevents 79, where it contacts the fibre bundle as it is advanced throughthe equipment and passes over the surface of the mandrel. Treatment ofthe fibres with steam at this stage increases the flexibility andpliability of the fibres, thereby pre-conditioning the fibres forfurther treatment in the treatment unit 80.

Treatment Unit

The treatment unit 80, positioned downstream of the mandrel assembly 60is in the form known to those skilled in the art as a steam block,illustrated in more detail in FIGS. 6A and 6B. The treatment unit is adie assembly that includes a die 84, in which the fibre bundle is formedinto its final configuration, and structural components for heating thedie and for treating the fibres with steam to cure the shaped fibrebundle.

The assembly comprises a housing 81 defining a hollow cuboidal chamberand is provided with a mounting bracket 82 by which the housing may bemounted for sliding movement back and forth along the downstream part ofthe rail 43. The treatment unit may be locked in any one of severaldiscrete locations along the rail defined by a row of bolt holes 44. Alocking pin on the mounting bracket 82 can engage with the bolt holes tosecure the treatment unit in a selected position on the rail 43.

The lateral faces of the housing 81 are each provided with an aperture83 a for receiving steam connectors (not shown) through which steam maybe introduced into the housing. The upstream and downstream faces of thehousing are each provided with an aperture 83 b for supporting acylindrical die 84. The die 84 is tubular, with a central axial passageof a diameter sufficient to receive the downstream segment 73 c of themandrel 73 and to define an annular gap between the mandrel 73 and thecylindrical wall of the passage equal to the desired annular thicknessof the tube of fibres.

The cylindrical wall of the die 84 is provided with passages 89 placingthe central axial passage of the die in communication with the exteriorsurroundings. The upstream end of the die carries a socket 85 with aninterior surface in the form of a cone that is tapered in the downstreamdirection form a diameter equal to or smaller than the downstream outletfrom the mandrel support 72, (e.g. 70%, 60%, 50%, or 40% smaller) to adiameter equal to the desired external diameter of the finished tubularfilter rods. The die 84 can be installed in the housing 81 so that itsdownstream end 86 projects out of the aperture in the downstream face ofthe housing, and the socket 85 is sealingly engaged in the aperture 83in the upstream face of the housing. A sealing plate 87, having acentral aperture 88 for receiving the downstream end of the die, may bebolted to the housing and sealed thereto by O-rings.

The treatment unit is constructed and arranged so that superheated steammay be passed from a supply line through the chamber of the housing 81via the apertures 83, by way of a valve (not shown) controlled from thecontrol panel 42. The steam may pass from the chamber through thepassages 89 in the die 84 and into contact with the fibres supported onthe downstream end of the mandrel 75, heating the fibres to atemperature at which they fuse together at their point s of contact,thereby fixing the fibres in their tubular configuration.

The fibre bundle is drawn through the equipment by take-off rollers (notshown) of conventional construction positioned downstream of thetreatment unit. The movement of the fibres through the equipment mayalso be assisted by means of a stuffer jet (not illustrated), locate forexample between the forming cone 50 and the mandrel assembly 60.

Use and Operation of Equipment and Manufacturing Process

The use of the equipment in a continuous manufacturing process forproducing tubular rods of fibrous material will now be described. Theprocess described broadly comprises gathering the fibres into a bundle,parting the fibres along the length of the bundle advances to form aradial cleft, advancing the bundle over a mandrel positioned in therecess, closing the fibres of the bundle around the mandrel, treatingthe bundle to fix the bundle in a tubular configuration, and removingthe bundle from the mandrel.

In the fibre supply module 1, the melt blowing head 10 is supplied withmolten polymer and hot gas. The molten polymer emerges as a liquidthrough the array of jets 13 and is blown by the hot air into thinstreams which solidify to form small diameter fibres 15 and becomeentrained in the gas stream.

The melt blowing head may be configured to produce mono-component fibresfrom a single polymer material or bi-component fibres having a coreformed from a first polymer encased in a sheath formed from a differentpolymer. For the production of tubular filter rods, mono-componentfibres may for example be formed from polyester, polyamide, ethyl vinylacetate, polyvinyl alcohol or cellulose acetate, optionallyincorporating other materials for modifying the properties of thepolymer, for example a plasticiser such as triacetin. Bi-componentfibres may be formed from any combination of compatible polymers, havingfor example, a core of polypropylene and a sheath of cellulose acetate,optionally incorporating a triacetin plasticiser.

Using air as the blowing gas, the die head is typically positioned 25-65cm above the upper run of the conveyor belt 29 and is operated with anair temperature of 250-350° C., e.g., 300-320° C., an air flow rate of500-600 cubic feet or 14,000-17,000 litres per minute, and a polymerthroughput of 0.3-0.5 grams per jet hole per minute. The resultingfibres typically have a diameter of 5-10 microns, e.g. about 7 micronsand can be gathered to form a tubular filter rod 5 having an externaldiameter of 5-10 mm, for example 7 to 9 mm, e.g. about 8 mm(particularly 7-7 mm), an internal diameter of 1 to 6 mm, for example 2to 5 mm and a weight of from 5 mg per millimetre length of the rod,typically from 8 to 12 mg/mm e.g. about 10 mg/mm.

The stream of gas and entrained fibres 15 is directed on to the conveyor24, and the fibres gather together in an entangled mat on the upper runof the conveyor belt 29 The conveyor 24 is operated to move the belt 29in the anticlockwise direction as seen in FIG. 2, thereby moving fibresout of the gas stream and downstream towards the forming module 3.

The resulting web 30 of gathered fibres is drawn continuously into andthrough the forming cone 50. FIG. 7A illustrates the generallyrectangular cross-sectional shape of the web of fibres 15 immediatelybefore it enters the forming cone 50. For example, the web may be 150 mmin width and 20 mm in thickness or “loft”. As the web travels throughthe forming cone, the fibres 15 are guided and compressed into a bundle32 of increasingly cylindrical shape. The cross-sectional shape of theweb at a point about half way thought the cone 50, indicated by thesection line 7B in FIG. 1, is illustrated schematically in FIG. 7B. Atthis point, as the web advances through the forming cone, thelongitudinal edges of the web are compressed towards the central axis ofthe forming cone, and the fibres are moved towards and over each otherboth laterally and vertically in a complex folding operation to lie oneither side of and below the divider rib 59 as they approach the tubularoutlet 57, which is of circular radial cross-section.

Within the forming cone, the density of the fibres within the bundleincreases progressively along the axis of the cone from a relatively lowdensity at the inlet to a higher density at the outlet 57. Thecross-sectional density of the bundle is not uniform. At each pointalong the length of the bundle, the fibre density increases in theradial direction from a void or low density region at the centre of thebundle to a higher density region at the periphery of the bundle.

As the web of fibres advances through the forming cone, the divider rib59 separates the fibres in the upper part of the bundle to form a cleft35 along the length of the bundle. In the embodiment illustrated, thedivider rib forms a cleft that penetrates up to and marginally beyondthe centre of bundle, making the depth of the cleft between 50 and 60%of the diameter of the bundle, e.g. about 55%.

As illustrated in FIG. 7C, when the bundle of fibres 15 emerges from theoutlet extension piece 58 of the forming cone, its envelope iscylindrical in shape with a diameter of about 15-25%, e.g. about 20% ofthe width of the web as it enters the forming cone and is formed with acleft 35 along its length.

The bundle then passes downstream from the forming cone into the mandrelassembly 60. FIG. 7D illustrates schematically, looking downstream, theconfiguration of the bundle of fibres 15 as it enters the mandrelassembly, the envelope of the bundle being indicated in broken lines.The divider plate 78 registers with the cleft 35 that has been formed inthe bundle of fibres upstream by the divide in the forming cone, andhold the cleft open as the fibres pass on either side of and below thedivider plate. The boss 76 on the tip of the upper mandrel rod 73 ainitiates an opening movement of the fibres at the centre of the bundleto make way for the upper mandrel rod 73 a, which is inserted into thecentre of the bundle and expands the fibres to form a central axialpassage 36 in the bundle of fibres.

As the bundle advances over the upper mandrel rod downstream from thedivider plate 78 and on to the lower mandrel rod 73 b, the cleft in thefibre bundle begins to close around the mandrel and the fibres form acontinuous peripheral layer around the wider diameter segment of thelower mandrel rod 73 b, as illustrated in FIG. 7E. At this point, thecentral passage 36 has a diameter larger than the desired internaldiameter of the finished tube, e.g. 10%, 15%, 20%, or 30% larger.

As the bundle advances downstream out of the mandrel support 72 and thecasing 71 towards the treatment assembly 80, it passes from thewider-diameter segment 73 b of the upper mandrel rod on to thesmaller-diameter segment 73 c of the lower mandrel rod, which has adiameter corresponding to the desired internal diameter of the finishedtubular rod. As the bundle approaches and enters the die 84, the taperedsocket 85 of the die 84 compresses the bundle of fibres around thedownstream segment 73 c of the mandrel, completing the closure of thecleft and producing a tubular structure about the mandrel with anexternal diameter corresponding to the desired external diameter of thefinished tube.

If a mandrel assembly constructed in accordance with FIGS. 5D and 5E isused, steam may be passed into the mandrel 73 and applied to the fibrebundle as it passes over the mandrel, thereby conditioning the fibresand facilitating compression around the lower mandrel rod 73 b as itenters the die 84.

FIG. 7F illustrates the configuration of the bundle of fibres at thepoint of entry into the socket 85 of the die, and FIG. 7G illustratesthe configuration of the tubular rod immediately downstream of the die84, after passing over the downstream end of the mandrel. Typically, theexternal diameter of the rod will be 10-20% e.g. 15% of the diameter ofthe bundle of fibres at the downstream end of the mandrel assemblyillustrated in FIG. 7E. The tubular structure emerging from the die hasthe desired internal and external diameters of the finished product.Tubes of different sizes and different combinations of internal andexternal diameters may be produced by using dies of different internaldiameters in combination with mandrels of different diameters.

As the bundle travels through the steam block whilst supported by themandrel, it is contacted under pressure, for example at a pressure of1-3 bar, typically about 1.5 bar, with superheated steam produced forexample by heating steam to a temperature in the range 150200° C. Thistreatment causes the fibres to bond together at their points of contact,thereby forming a bonded, self-supporting structure in the form of atubular rod 5, as illustrated in FIG. 7G.

The rod 5 may then be drawn from the mandrel and then through furtherprocessing equipment for example an air block, to remove excess waterfrom the rod, and a cutting machine which severs the rod intoconsecutive tubular segments of a desired length, as illustrated in FIG.7F.

In the embodiments of the process disclosed herein, a critical point inthe process is the insertion of a mandrel into the centre of the fibrebundle, with the objective of forming a central support around which atubular structure can be formed. A risk arises in the use of a mandrel,particularly when the process is operated at high speed, that the fibresfail to distribute themselves uniformly around the mandrel, and collapseinto a non-tubular structure, non-cylindrical structure. In theembodiments described herein however, the formation of a cleft in thefibre bundle before it is passed over the mandrel controls andstabilises the movement of the fibres into a tubular configuration,facilitating the formation of a tubular structure, and reducing theincidences of collapse of the tubular structure.

1. A method of forming a tubular rod of fibrous material comprisinggathering fibres into an elongated bundle, parting the fibres to form acleft along the length of the bundle, introducing a mandrel into thecleft, closing the fibres of the bundle around the mandrel in a tubularconfiguration, and separating the fibres from the mandrel as a tubularrod.
 2. A method according to claim 1 wherein the cleft is formed as arecess extending partially through the bundle.
 3. A method according toclaim 1 or claim 2 wherein the cleft is formed to extend radially fromthe periphery of the bundle to the centre of the bundle.
 4. A methodaccording to any one of claims 1 to 3 wherein the cleft is formed toextend 50%, 60%, or 70% of thickness of the bundle.
 5. A methodaccording to claim 1 wherein the cleft divides the bundle into twoparts.
 6. A method according to Any one of claims 1 to 5 wherein atreatment fluid is delivered to the bundle of fibrous material as itpasses over the mandrel.
 7. A method according to claim 6 wherein thetreatment fluid is delivered from within the mandrel.
 8. A methodaccording to any one of claims 1 to 7 wherein the fibres are suppliedfrom a feedstock of fibrous material.
 9. A method according to any oneof claims 1 to 8 wherein the fibres are supplied by a continuousmanufacturing process.
 10. A method according to any one of claims 1 to8 wherein the fibres are produced by a melt-blowing process
 11. A methodaccording to any one of claims 1 to 10 wherein the bundle of fibres istreated to fix the bundle in a tubular configuration
 12. A methodaccording to claim 11 wherein the bundle of fibres is advanced through aconstriction that defines a desired circumferential profile for thebundle of fibres, and a treatment fluid for curing the fibres isintroduced into the bundle as the fibres enter the constriction. 13.Equipment for forming a tubular rod of fibrous material comprising:gathering equipment constructed to receive a continuous supply of fibresand to gather the fibres into a bundle as the fibres advance through theequipment; a divider arranged in the path of the fibres through theequipment and constructed to from a cleft along the length of the bundleas it advances through the equipment; a mandrel positioned in the pathof the bundle of fibres in alignment with the divider and constructed toform the cleft into a passage through the bundle of fibres as the bundleof fibres advances over the mandrel; and a die constructed and arrangedto cooperate with the mandrel to form the fibres in a tubularconfiguration around the mandrel.
 14. Equipment according to claim 13wherein the gathering equipment comprises a forming cone having an inletfor receiving the fibres, an outlet from which the web of fibres may bewithdrawn as a bundle, and the forming cone defines a longitudinallyextending passage of tapering configuration between the inlet and theoutlet.
 15. Equipment according to claim 14 wherein the dividercomprises a projection in the passage of the forming cone extendingbetween the inlet and the outlet.
 16. Equipment according to any one ofclaims 13 to 15, wherein the mandrel is mounted in an open-ended tubularcasing configured to receive the bundle of fibres.
 17. Equipmentaccording to claim 16 wherein the divider comprises a support connectingthe mandrel to the tubular casing.
 18. Equipment according to any one ofclaims 13 to 17 wherein the mandrel comprises a passage for delivering atreatment fluid to the bundle of fibrous material the as the bundlepasses over the mandrel.
 19. Equipment according to any one of claims 13to 18 wherein the die is constructed and arranged to form the fibresaround the mandrel into a desired external shape.
 20. Equipmentaccording to claim 19 wherein the die comprises a body having a centralpassage therethrough, and the mandrel comprises a rod mounted within thecentral passage to define a tubular space between the body and themandrel.
 21. Equipment according to any one of claims 10 to 20 furthercomprising a treatment station in which the fibres may be cured whilstsupported on the mandrel.
 22. Equipment according to claim 21 whereinthe treatment station comprises a housing defining a chamber into whicha treatment fluid may be introduced, and the die is positioned withinthe housing and is provided with one or more conduits for delivering thetreatment fluid from the chamber to the fibres.